Yeah, I have to agree because he looked way past 58 and we know that smoking does age you faster. I, a non smoker, was shocked to discover that I'm older (by 2 years) than he was. In any event, he was the consummate professional, quite credible in every role he took on. RIP.
This is from his IMDB biography:
"John had been an acknowledged alcoholic, who remained sober ever since getting therapy. He had quit smoking in 1999, which he described as 'hell on earth'."
I guess the years of damage had taken their toll. I agree that he was a pro, probably even a workaholic, which may have also contributed to his demise.